4GB Flash drives only shows up at 2GB

I have a 4gb Kingston USB stick but when I plug it into windows, it only shows up as 2GB. Under disk management, I can see the remaining 2GB but can't format or delete it. I can only format/delete the first 2GB. What can I do to be able to use all 4GB? I'm running Windows 7 ultimate of that makes any difference.

Had the same problem for no obvious reason. Have used this SD card over and over and this happened all of the sudden. The HP utility worked perfectly! Hope other people find this thread useful. Thanks tipstir!